1. Field of the Invention
The present invention is directed to an exhaust system for a watercraft, and more particularly to a water preclusion and noise attenuation system employed in a watercraft exhaust system.
2. Description of Related Art
Personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries a rider and possibly one to three passengers. A relatively small hull of the personal watercraft commonly defines a riders' area above an engine compartment. A two-cycle internal combustion engine frequently powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the watercraft hull. The jet propulsion unit is located within the tunnel and is driven by a drive shaft. The drive shaft usually extends between the engine and the jet propulsion device, through a wall of the hull tunnel.
Because of their small size and high degree of maneuverability, however, there are certain objections to the use of these watercraft on some bodies of water. One of these objections is caused by the fact that this type of watercraft, primarily because of its small size, has a relatively simple exhaust system that does not provide a significant degree of silencing. This result is mandated primarily by the very compact nature of the watercraft and the relatively small area that is available for exhaust treatment. Because these watercrafts can be utilized on quite small bodies of water, the potential noise may be more objectionable than larger watercraft having unmuffled exhaust systems but which do not operate on these small bodies of water.
An exhaust system of a typical personal watercraft discharges engine exhaust to the atmosphere either through or close to the body of water in which the watercraft is operating. Although submerged discharge of engine exhaust silences exhaust noise, environmental concerns arise. These concerns are particularly acute in connection with two-cycle engines because engine exhaust from two-cycle engines often contains lubricants, unburned fuel, and other byproducts.
Such environmental concerns have raised a desire to minimize exhaustion of hydrocarbons and other exhaust byproducts (e.g., carbon monoxide and oxides of nitrogen), and thus reduce pollution of the atmosphere and the body of water in which the watercraft is operated. In response to the increased concerns regarding exhaust emissions, some personal watercraft engines recently have been equipped with a catalyst to convert exhaust byproducts to harmless gases.
Catalysts must operate at a relatively high temperature in order to produce the necessary thermal reaction and burning of the exhaust byproducts. A catalytic device thus desirably operates within a specific range of temperature so as to effectively and efficiently convert engine exhaust into generally harmless gases.
Some prior exhaust systems have employed a cooling jacket about the catalytic device to maintain the catalytic device within the desired temperature range. In some systems, at least a portion of the cooling water also is introduced into the stream of the exhaust gasses discharged from the engine, not only further cool and silence the exhaust gases, but also to assist the discharge of exhaust gases. The added water to the exhaust system, however, gives rise to possible damage to the catalyst.
In order to prevent water from entering the exhaust system which could therefore damage the engine and/or catalyst, it is been known to provide watercraft with a device commonly referred to as a "watertrap" (a.k.a. "waterlock" or "water box"). A watertrap typically includes an inlet, an outlet, and a plurality of baffles defining open chambers which under certain operating conditions contain water. Typically, the watertrap is arranged in the exhaust system downstream from the engine exhaust manifold and upstream from a discharge port of the exhaust system. The exhaust gases and water flow through the chambers within the watertrap while the chambers generally prevent water from moving back through the watertrap and upstream through the exhaust system towards he engine exhaust manifold and/or the catalyst during abrupt watercraft movements or if he watercraft is capsized. If a watercraft is capsized, a significant amount of water may flow into the watertrap from the portion of the exhaust system piping downstream from the watertrap, thereby forcing a substantial amount of water upstream into the exhaust system and fowling and/or damaging the internal combustion engine and/or shattering the catalyst bed of the exhaust system.
Exhaust noise also posses problems for personal watercraft use. Despite recent attempts to reduce the noise generated by and emissions discharged from personal watercraft powered by two-cycle engines, certain recreational facilities have banned the operation of two-cycle watercraft. Such bans have resulted in a decrease in popularity of personal watercraft powered by two-cycle engines.